Axial field electric direct current motor and generator

ABSTRACT

An electrical direct current machine ( 10 ), which can be operated as a motor and as a generator and works according to the axial field principle. The machine has a rotor ( 26 ), which is rotatably mounted in a housing ( 12 ), has a plurality of electromagnets mounted at a distance from the axis of rotation, with in each case one coil winding ( 34 ) of a coil core ( 32 ) carrying one or more electrical conductors, the ends of the electrical conductors, forming the coil, being taken radially inward and being connected in an electrically conductive manner with, in each case, assigned contact elements having in each case one contact surface and, taken together, forming a commutator, on which contact elements sliding contacts ( 42 ) are pressed against a source or a consumer of direct current. At regular angular distances, pole faces of permanent magnets, with in each case opposite polarity in the circumferential direction, are provided consecutively on the insides of the housing end walls ( 14   a;    14   b ). At uniform angular distances, pole faces of permanent magnets, which are disposed on the inner sides of the end walls ( 14   a;    14   b ) of the housing opposite the end surfaces of the coil cores ( 32 ) are provided with consecutively in each case opposite polarity in the circumferential direction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an electric direct current machine.

2. Description of the Related Art

An electric direct current collector machine, which can be used as amotor as well as a generator, is known (for example, from DE 33 24 617A1). For this collector machine, a rotor, carrying a plurality ofnon-ferrous coils of electrical conductors at uniform angular intervalson the same diameter, is rotatably mounted in one housing. On the innersides of the end surface of the housing, rigidly disposed permanentmagnets of polarity, differing consecutively in the circumferentialdirection, are located opposite to and on either side of the coils. Theconductors, forming the coils, are connected in turn to commutatorcontact surfaces, which rotate with the rotor and are insulatedelectrically from one another and on which sliding contacts, which areprovided in the housing and insulated from the wall of the housing andwhich are connected conductively with external electrical connections,are pressed. When connected to an electric direct current source, themachines, so constructed, act as a motor. On the other hand, when therotor shaft is driven, they act as a generator, that is, electricaldirect current can be collected from their terminals. These known directcurrent machines find use, for example, as small, very compact motors oflow output, for example, as motors for driving recording devices forvideo signals. Because of the special arrangement of the rotor coils andthe permanent magnets and the therefrom resulting course of theinteracting fields of the permanent magnets and the rotor coils, suchmotors are also referred to as axial field machines. Because of the goodefficiencies that can be attained with them and because of the basicallygood possibilities of regulating them, such axial field machines, withlarger dimensions and a correspondingly higher output, have also beenproposed, for example, as driving motors for vehicles (WO 95/17779).

SUMMARY OF THE INVENTION

It is an object of the invention to further the development of such anelectric direct current machine with higher outputs, which makes it alsosuitable as driving motors for vehicles, so that the machine, whilehaving a simple and therefore cost-effective construction, achieves ahigh efficiency.

Pursuant to the invention, this objective is accomplished by an electricdirect current machine with a rotor, which is rotatably mounted in ahousing, has a plurality of electromagnets mounted at a distance fromthe axis of rotation, with in each case a coil winding on a coil corecarrying one or more electrical conductors, the ends of the electricalconductors, forming the coil, being taken radially inward and beingconnected in an electrically conductive manner with, in each case,assigned contact elements having in each case one contact surface and,taken together, forming a commutator, onto which contact elementssliding contacts are pressed, which are held in the housing and can beconnected to a source of direct current or to a direct current consumer,and with pole faces of permanent magnets, which are disposed at regularangular distances on the inner sides of the end walls of the housingopposite the end faces of the coil cores and, consecutively in thecircumferential direction, have opposite polarities, each coil coreforming with the associated coil winding a separately producedelectromagnet component, which is held in a hub support, which isconnected with the shaft of the rotor so that there can be no mutualrotation, the pole faces of the permanent magnets extending so that theyoverlap in each case several opposite coil cores, the two slidingcontacts of the commutator, assigned to a radially external permanentmagnet, extending so far in the circumferential direction, that theyoverlap the contact surfaces, of in each case, about half of the contactelements assigned to a pole face of a permanent magnet, and contactsurfaces being provided, which are offset to the contact surfaces of thecontact elements forming the commutator and connected electrically withthe respective contact surfaces on the commutator side and against whichsliding contacts are pressed, which essentially correspond in thecircumferential extension to the sliding contacts of the commutator andin turn are connected electrically with one another in each case inpairs.

The prefabrication of the electromagnet components and their subsequentmounting in the hub support ensures the desired simple construction andthe cost-effective mounting. Due to the refinement that in each caseseveral electromagnet components are assigned to each permanent magnet,it is possible to energize the electromagnet component, which runs intothe field of a permanent magnet when the rotor is running, in such amanner, that they have an opposite polarity and thus are attracted bythe electromagnet in the circumferential direction. As soon as the coilcore of the respective electromagnet component is then aligned centrallyto the permanent magnet, the polarity of the coil core is reversed overthe contact surfaces opposite to the commutator contact surfaces, as aresult of which the electromagnet component then has the same polarityas the opposite permanent magnet and is thrust further in the directionof rotation.

At the same time, it may be appropriate if the contact surfaces of thesliding contacts of the commutator and the contact surfaces of thesliding contacts, which are assigned to the commutator sliding contactsand connected electrically with one another in pairs, can be shiftedrelative to one another by a specified amount in the direction ofrotation of the rotor. In this way, the effective contact surface ofsliding contacts of the commutator in the circumferential direction and,with that, the characteristics of the direct current machine can bechanged.

Preferably, the coil cores have the shape of essentially rectangulardisks, which extend radially and parallel to the rotor axis and the edgeregions of which protrude with the radially extending end edges over thecoil winding carried by them. These protruding edge regions of the coilcores then act—particularly if they are aligned in the radialdirection—like radial blades of a blower, which enables a motor to becooled by aspirating from the surroundings in the radially inner regionof the housing and blowing it out in the radially outer region of thehousing. The radial and disk-shaped construction of the coil coresfurthermore makes it possible to provide a large number of electromagnetcomponents on a specified diameter, especially if the machine inquestion is developed on the axial field principle with a relativelylarge diameter and does not extend very far axially. Moreover, anoptimum utilization of space is attained if the coil cores of asectional plane, placed at right angles through the rotor shaft, has across section diverging from the radially inner boundary edge to theradially outer boundary edge.

The electrical conductors of an electromagnet component can be formedfrom an extended electrical conductor, such as a metal strip of a copperalloy, which is passed in at least a half turn around the coil core. Arotor, assembled from such electromagnet components, then has sufficientinherent stability, that is, it requires no or only a skeleton-likerotor framework, so that air can flow well through the electricconductors and the rotor can thus be cooled.

Alternatively, the electrical conductors of the electromagnet componentscan also be formed from a plurality of electrically conducting metalwires, which lie next to one another and are passed around the coil corein at least half of a winding.

The coil cores of the electromagnet components can be disposed at aradial distance from and essentially parallel to the axis of rotation ofthe rotor.

Alternatively, the coil cores of the electromagnet components can alsobe disposed at a radial distance from and inclined at such an angle tothe axis of rotation of the rotor, that their opposite end faces,pointing to the permanent magnets, are offset to one another in thecircumferential direction. At the same time, the distance in the radialdirection of the opposite end faces of the coil cores from the axis ofrotation of the rotor can be the same.

On the other hand, the formation can also be such that the coil cores ofthe electromagnet components are disposed at a radial distance from andinclined at such an angle to the axis of rotation of the rotor, thattheir opposite end surfaces, pointing towards the permanent magnets, areat a different distance, in the radial direction, from the axis ofrotation of the rotor.

A further development serves for the stabilization of the electromagnetcomponents in the rotor as well as for the formation, laterally to theend walls of the housing, of closed chambers, through which air can flowradially for cooling as if driven by a blower. For this furtherdevelopment, the coil cores of all electromagnet components areconnected to one another by, on each side in each case, one ring disk ofmagnetically not magnetic material, which is provided in the end regionsin the coil core close to the end faces. In this connection, theopposite end faces of the coil core advisably pass through the ring diskassigned in each case, so that the gap between the end faces of the coilcore and the pole faces of the permanent magnets can be kept as small aspossible.

An appropriate and advantageous development of the permanent magnets isobtained if, in each case, two pole faces of different polarity of thepermanent magnets, which are consecutive in the circumferentialdirection and face the rotor, are formed from the two parallel polefaces, pointing into the interior of the housing, of a permanent magnetshaped in the form of a horseshoe magnet.

Moreover, this permanent magnet, formed in the shape of a horseshoemagnet, can be formed by the end faces, facing the rotor, of softmagnetic pole shoes, which are passed through the end walls of thehousing consisting of a non-magnetic material and which are coupledoutside of the respectively assigned end wall of the housing to in eachcase one pole of a permanent magnet. The permanent magnets may then beformed simply as conventional rod magnets.

In this connection, the pole shoes are advantageously formed frompackages of transformer sheets held against one another in tight contactyet insulated electrically, in order to minimize losses due to eddycurrents. If the permanent magnets are formed from pole shoes with a rodmagnet, it is advisable to hold the opposite ends of the rod in, in eachcase, one seat in the respective pole shoe formed at least partially ina complementary fashion to the end of the rod.

One embodiment of the pole shoe, which can be adjusted parallel to theaxis of rotation of the rotor and fixed within a specified adjustmentrange, in the respectively assigned end wall of the housing, permits thedistance between the end faces of the coil cores of the electromagnetcomponents of the rotor and the pole faces of the permanent magnets,formed by the end faces of the pole shoes within the housing, to beadjusted to a barely still permissible slight extent and, in this way,makes it possible to optimize the efficiency of the machine itself.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in greater detail in the followingdescription of several examples and in conjunction with the drawing, inwhich

FIG. 1 shows, in a so-called half section, that is, in the lower half inside view and in the upper half as a section along a radial plane, anexample of a direct current machine, which is constructed in theinventive manner and shown diagrammatically,

FIG. 2 shows a view of the inside of an end wall of the housing,carrying the permanent magnets, seen in the direction of arrow 2—2 inFIG. 1,

FIG. 3 shows a view of the rotor of the direct current machine, built upfrom a plurality of electromagnet components, seen in the direction ofthe arrow 3—3 in FIG. 1,

FIG. 4 shows a diagrammatic representation of the pole reversal circuitof successive electromagnet components of the rotor of an inventivedirect current generator,

FIG. 4a shows a diagrammatic representation of mutually assigned slidingcontacts of a pole reversal circuit, when looking towards their contactfaces,

FIG. 5 shows a side view of a first example of an inventiveelectromagnet component,

FIG. 6 shows a view of the electromagnet component, seen in thedirection of arrow 6 in FIG. 5,

FIG. 7 shows a side view of a modified example of an electromagnetcomponent,

FIG. 8 shows a view, shown in the direction of arrow 8 in FIG. 7,

FIG. 9 shows a modified electromagnet component, for which, instead ofstrip-shaped metal conductors, several parallel wires have been providedas a coil winding for the one on the coil core,

FIG. 10 shows a view, seen in the direction of arrow 10 in FIG. 9,

FIG. 11 shows a side view of a modified electromagnet component, alsobuilt up using a plurality of parallel metal wires arranged next to oneanother,

FIG. 12 shows a view seen in the direction of the arrow 12 in FIG. 11,

FIG. 13 shows a view, corresponding to the direction of viewing in FIG.2, of the inside of an end wall of a housing with a modified developmentand arrangement of the permanent magnets and

FIG. 14 shows a view of the partial sections of the end walls of thehousing located within the arcs illustrated in FIG. 13 by the arrows14—14 and of the rotor of an example of an inventive direct currentmachine modified from the example of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIGS. 1 to 3, an example of an inventive direct current machine,which is labeled 10 as a whole and can be used as a motor and as agenerator, is shown in diagrammatic representation. In the specificcase, the machine 10 has a housing 12, which is relatively short in theaxial direction and is composed of two disk-like housing end walls 14 a,14 b of relatively large diameter and of the actual peripheral wall 16of the housing, converted practically into a cylindrical ring ofrelatively small length. The end walls 14 a, 14 b of the housing andperipheral wall 16 of the housing are connected with one another, sothat they can be dismantled, by screws or other fastening means, whichare not shown.

Central passage openings 15 a, 15 b in the end walls 14 a, 14 b areclosed off by the housing lid 18 a, 18 b, in which in each case abearing seat 20 for a journal type radial bearing 22, in which a shaft24 passing through the cover 18 a of the housing is rotatably mounted,is formed centrally. This shaft 24 carries the rotor 26, which is heldon it so that there can be mutual rotation (FIG. 3).

On the inner end faces of the end walls 14 a, 14 b of the housing,permanent magnets 28, placed radially at uniform angular distances asfar as possible to the outside, are disposed on radii identical withrespect to the center line of the housing. In the case shown (FIG. 2),the end walls 14 a, 14 b each carry twelve permanent magnets.Consecutive permanent magnets in the circumferential direction haveopposite polarity.

The rotor 26 (FIG. 3) is assembled from a plurality of electromagneticcomponents 30, which are produced initially as separate, individualcomponents. In the example shown, they comprise a total of seventy-twocomponents 30. In FIGS. 5 and 6, such a component 30 is shownseparately. Each electromagnet component 30 has a coil core 32, which isconstructed as a disk of a soft magnetic material and over which a totalof two windings of a metal strip, which is produced advisably from acopper alloy of high electric conductivity, are wound as a coil winding34. In the region forming the winding on the coil core, the strip isinsulated in the usual manner, for example, by a non-conductivelacquering, from the coil core and adjoining components 30. The coilcore 32, in turn, is built up in the usual manner from transformersheets, which are insulated from one another and packed to largelysuppress eddy currents. The two ends 36 a, 36 b of the strip 36 of eachelectromagnet component 30 are taken radially towards the inside in thedirection of the shaft 24 and held there in a hub support 38, which has,for example in the manner indicated in FIG. 1, two plastic ring objects38 a, 38 b of insulating material, which are mutually offset axially andeach hold one of the ends 36 a or 36 b of the components 30. The stripends 36 a, 36 b of all electromagnet components 30 are cast into thesering objects 38 a, 38 b and held insulated from one another. The rotor26 is connected, so that there can be mutual rotation, with the shaft 24by means of a wedge connection, which is indicated, for example, in FIG.1 by a wedge-shaped groove 40. If a suitable material of the appropriatedimension is selected for the strip 36, the rotor 26, formed by the hubsupport 38 and the plurality of electromagnet components, is selfsupporting. Alternatively, however, an additional stiffening of therotor is conceivable by partially filling up the spaces between theradially extending conductor strips 36. The disk-shaped coil cores 32protrude in the axial direction beyond the coil winding 34, so that,when the rotor is running, they bring about an air flow in the housing,which is directed from the inside to the outside. By means of suitable(not shown) air-supplying ducts in the end walls 14 a and/or 14 b andair-discharging openings in the actual housing 16, circulation of thesurrounding air, automatically ensuring the cooling of the generator, isforced when the generator is running. By means of ring disks 41 of amagnetically non-conducting material, placed on either side on theregions of the coil cores 32 protruding axially beyond the coil winding34, the circulation of the surrounding air can be concentrated on thespaces between the electromagnet components 30 and the cooling actioncan thus be optimized. At the same time, these ring disks 41 stabilizethe electromagnet components, in that they fix them relative to oneanother at a specified radial distance from the axis of rotation of therotor as well as at a distance from one another in the circumferentialdirection.

The electromagnet components 30 of the machine 10 are connected to anexternal source of direct electric current, such as accumulator or, inthe event that the machine is used as a generator, to a consumer ofdirect current, over sliding contact 42 which, in accordance with therepresentation of FIG. 1, can be constructed as carbon brushes, pressedby springs 44 directly against the end edges of the radial sections ofthe conductor strips 36, which are not insulated. The not insulated endedges of the strips 36 of all electromagnet components 30, takentogether, form the commutator at the rotor 26 of the machine 10.Alternatively, the commutator can also, of course, be formed by contactelements, which are mounted separately at the conductors forming thecoil winding, in the event that this is desirable, for example, withrespect to the wear of the contact surfaces. In conjunction with FIGS.9, 10 and 11, 12, electromagnet components are described below, forwhich separate contact elements for the commutator are connected, forexample, by welding, to the conductors forming the coil winding. Fromthe above description of the direct current machine 10, it is clear thatthe permanent magnets 28, which are provided at the end walls of thehousing and are opposite to the coil cores 32 of the electromagnetcomponents 30, extend to such a degree in the circumferential direction,that more than three electromagnet components are located opposite tothem at any given time. The electromagnetic components are provided withcurrent by the commutator in such a manner, that the polarity of thecoil core of an electromagnetic component entering between a pair ofassociated permanent magnets is opposite to that of the associatedpermanent magnets, so that the respective component 30 is pulled by themagnetic interactions between the permanent magnets is reached, areversal of the polarity of the electromagnet components 30 then takesplace so that a repulsion and, with that, an unavoidable furtherrotation of the rotor is brought about by the opposite polarization ofthe coil core, which then takes place. This is attained by the circuitshown diagrammatically in FIG. 4. In the drawing, two electromagnetcomponents 30 are shown, which are offset to one another in thecircumferential direction, but still assigned to the same permanentmagnets in the peripheral extent, and are connected over leads 46 to theassociated source of direct current 48, such as an accumulator. In thiscase, the sliding contacts 42 have a peripheral extent, whichcorresponds, at most, to half the circumferential extent of a permanentmagnet 28, so that the energizing of the respective coil core 32 takesplace over the respective lead 36 in the aimed-for sense in such amanner, that the respective component 30 is attracted during the firsthalf of the entry between a pair of permanent magnets 28 belongingtogether. As soon as the respective coil core 32 has moved beyond thecenter of the momentarily opposite pair of permanent magnets 28, theflow of current from the source 48 of direct current is reversed over apair of sliding contacts 50, which are connected electrically with oneanother, so that the polarity of the magnetic field, generated in therespective coil core 32, is reversed and then is equal to the polarityof the opposite pair of permanent magnets. The coil core 32 and, withthat, the electromagnet component 30 are then displaced from theassociated pair of magnets 28, that is, the rotor 26 receives animpulse, displacing it further in the direction of rotation.

FIG. 4a furthermore illustrates diagrammatically that the slidingcontacts 42 and 50, which are assigned to one another and the contactsurfaces of which are bounded approximately trapezoidally, can also beoffset to one another in the direction of rotation of the rotor. In thecase shown, current can flow only in the electromagnet components 30,against the commutator surfaces of which the cross-hatch region 42 a ispressed, in which the contact surfaces 42 and 50 overlap. By changingthe arrangement of the contact surfaces of the sliding contacts 42, 50,which are twisted relative to one another, the effective contact surfacecan thus be enlarged or decreased and the characteristics of the directcurrent machine with respect to the rpm/torque behavior can be changedand, in this manner, adapted to different requirements. Moreover, it iseven possible to consider developing the possibility of a relativetwisting of the sliding contacts, assigned to one another, manually orby an automatic control, variably during the operation, in order toadapt the rpm or the torque deliberately or automatically in this mannerto different conditions.

In FIGS. 7 and 8, a modification, labeled 130 as a whole, of theelectromagnet component 30, which has already been described and isportrayed in FIGS. 5 and 6, is shown. The electrical conductorsurrounding the coil core 132 with only half a winding here, once againhas the shape of a correspondingly wider strip 136 of highly conductivemetal, the ends 136 a, 136 b of which are machined in such a manner atthe respectively opposite end edges, that on each side only the end edgeof one of the ends is accessible for contact with a sliding contact 142.Thus, taken together, the machined end regions 136 a, 136 b of theelectromagnet components 130 once again form the commutator. It isimportant that the mutually facing inner surfaces of the conductor strip136 are insulated from one another and from the coil core 132 by asuitable coating.

The modification of an electromagnet component 230, shown in FIGS. 9 and10, differs from component 30 owing to the fact that, instead of thestrip-shaped conductor 36 for the coil winding 234, a number of copperwire conductors 236, connected in parallel, are provided, which in thespecial case are taken in two windings about the coil core 232. Theends, taken radially inwards, are held in separate, metallic contactelements 236 a, 236 b, for example, by welding. These metallic contactelements of the electromagnet components 230 together once again formthe commutator. In addition, they can also be constructed for fixing thecomponents 230 in the hub body of the rotor. In this case, the coil core232, in turn, is shaped from a block of transformer sheets, which areinsulated from one another, stacked on top of one another and connectedtogether by mechanical machining in such a manner, that the blockexpands outwards in the radial direction and thus, with respect to thecross section of the core, optimally utilizes the space available in thehousing. The regions, protruding over the coil winding 234 laterallytowards the outside, are enlarged compared to the region carrying thecoil winding 234, so that the coil winding is secured against lateralmigration on the coil core 232.

Finally, in FIGS. 11 and 12, a modification of the electromagnetcomponent 130, labeled 330, is shown, for which, once again, thestrip-shaped conductor 136 is replaced by a plurality of parallel copperwires 336. The wires, passed in tight proximity about the coil core 232are, in turn, for example, once again soldered or welded at the ends incontact elements 336 a, 336 b, which protrude at opposite sides andopposite directions, so that they once again form at the end face thecontact surfaces for commutator sliding contacts. The copper wires canbe insulated in the usual manner by an insulating lacquering in theregions, in which they are in contact with one another and passed overthe coil core 332, the insulating separating layer 332, which is to beprovided between the contact elements 336 a, 336 b, being taken furtherbetween the two parallel copper wire sections up to the coil core 232.Aside from ensuring that the contact elements 336 a, 336 b and thecopper wires are insulated from one another, this insulating layer canalso increase the stiffness of the electromagnet component 330 as awhole. The copper wires 336 are prevented from sliding off the coil core332 by being provided with short protruding shoulders 333 in theprotruding regions.

In FIGS. 13 and 14, an advantageously modified example of the embodimentof the housing 12 of the example of the inventive direct currentmachine, described in conjunction with FIGS. 1 to 3, is shown. Themodification-made relates, particularly, to the construction of thepermanent magnets. In the case of the previously described example,flat, plate-shaped permanent magnets 28 with consecutively alternatingpolarity are disposed on the inside of the housing end walls 14 a, 14 b,facing the rotor. On the other hand, in the case of the modifiedexample, in each case two permanent magnets, following one another inthe circumferential direction, are formed from the pole ends of apermanent magnet 60, shaped in the form of a horseshoe magnet. The poleends of the permanent magnet 60, formed in the special case fromseparate pole shoes 62 a, 62 b, are themselves soft magnetic components,which are produced from layered transformer sheets and pass throughsuitable openings 64 in the housing end walls 14 a, 14 b, produced froma non-magnetic material, such as a plastic. On the outside, averted fromthe rotor, the two pole shoes 62 a, 62 b are then connected by theactual permanent magnets, which are constructed as rod magnets 66. Byconstructing suitable seats 68 in the pole shoes 62 a, 62 b, that is,seats 68 into which the ends of the rod magnet 66 fit, optimum magneticcoupling of the rod magnets to the pole shoes 62 a, 62 b is ensured. Bya holding mechanism for the pole shoes 62 a, 62 b in the openings 64 ofthe end walls 14 a, 14 b, which holding mechanism is not shown in detailin the drawing and can be fixed in selectable adjustments, the gap forensuring the best possible efficiency, which is required forconstructive reasons between the end surfaces of the coil core 32 of theelectromagnet components 30 and the end surfaces of the pole shoesfacing these components 30, can be optimized.

It is evident that, within the scope of the inventive concept, it ispossible to realize modifications and further developments of theexamples described, which relate to the design of the electromagnetcomponents as well as to the method for holding and fastening them inthe hub body and to the construction of the commutator.

For example, the shape, particularly the cross-sectional shape, of thecoil cores of the electromagnet components can deviate even from thedisk-shaped configuration described. If a lesser number of electromagnetcomponents are to be assembled into a rotor, simple, rod-shaped coilcores with, for example, a circular cross section can also be provided.

Deviating from the arrangement of coil cores described, which isparallel with respect to the axis of rotation of the rotor, it may alsobe meaningful to dispose the coil cores at a slight angle to thecircumferential direction and/or inclined to the radial direction.

What is claimed is:
 1. An electric direct current machine comprising: ahousing comprising two parallel end walls; a rotor, comprising a shaft,rotatably mounted in said housing perpendicular to said end walls; aplurality of electromagnets mounted between said end walls at apredetermined distance from the axis of rotation of said rotor, each ofsaid electromagnets comprising one or more electrical conductors forminga coil winding on a coil core, each electrical conductor comprising atleast one connect surface; a plurality of permanent magnets, comprisingopposite pole faces, disposed at regular angular distances on said endwalls, said pole faces being opposite end faces of said coil core, witheach consecutive permanent magnet in the circumferential directionhaving opposite polarities; and a plurality of contact elements assignedto said permanent magnets, each comprising at least one sliding contacthaving a contact surface; wherein the ends of the electrical conductorsforming the coils of said electromagnets are taken radially inward andconnected in an electrically conductive manner with said assignedcontact elements, thus forming a commutator, by pressing the slidingcontacts of said contact elements onto the connect surfaces of saidelectrical conductors, said contact elements being held in the housing;wherein said contact elements on one side of said electromagnets,forming the commutator, being for connecting to a source of directcurrent or to a direct current consumer, and said contact elements onthe opposite side of said electromagnets being connected to one anotherin pairs; wherein each of said electromagnets is held in a hub support,which is connected with the shaft of the rotor so as to insure mutualrotation; wherein each pole face of the permanent magnets overlapsseveral opposite coil cores; and wherein the contact surfaces of thesliding contacts of the commutator assigned to one of said permanentmagnets overlap about half of the contact surfaces of the slidingcontacts of the corresponding contact elements assigned to a pole faceof a corresponding permanent magnet on the opposite side of theelectromagnets, said overlapping opposite contact surfaces being offsetto one another.
 2. The direct current machine of claim 1, wherein theoverlapping opposite contact surfaces can be adjusted relative to oneanother in the direction of rotation of the rotor.
 3. The direct currentmachine of claim 1, wherein the coil cores have a shape of essentiallyrectangular disks, said rectangular disks having an edge region whichprotrudes in an axial direction beyond said coils on said disks.
 4. Thedirect current machine of claim 3, wherein the coil cores, in relationto a plane intersecting the axis of rotation of the rotor at rightangles, have a cross section diverging from a radially inner boundaryedge to a radially outer boundary edge.
 5. The direct current machine ofclaim 1, wherein the electrical conductors of the electromagnetcomponents are formed by at least one extended strip of electricallyconducting metal, passed around the coil core in at least half awinding.
 6. The direct current machine of claim 1, wherein the electricconductors of the electromagnet components are formed by a plurality ofelectrically conducting metal wires, which lie next to one another andare passed around the coil core in at least half of a winding.
 7. Thedirect current machine of claim 1, wherein the coil cores of theelectromagnet components are disposed at a predetermined radial distancefrom and essentially parallel to the axis of rotation of the rotor. 8.The direct current machine of claim 1, wherein the coil cores of allelectromagnet components are connected to one another by, on each sidein each case, one ring disk, which is made from a material that is notmagnetic and is provided in the end regions of the coil core close tothe end faces.
 9. The direct current machine of claim 8, wherein theopposite end surfaces of the coil cores pass through the ring diskassigned in each case.
 10. The direct current machine of claim 1,wherein in each case two pole faces of different polarity of thepermanent magnets, consecutive in the circumferential direction andfacing the rotor, are formed from the two parallel pole faces, pointinginto the interior of the housing, of a permanent magnet shaped in theform of a horseshoe magnet.
 11. The direct current machine of claim 10,wherein the end faces of the permanent magnets, facing the rotor, areformed at soft magnet pole shoes, which are passed through the end wallsof the housing consisting of a non-magnetic material and are coupledoutside of the end walls of the housing to in each case one pole of apermanent magnet.
 12. The direct current machine of claim 11, whereinthe pole shoes are formed from packages of transformer sheets heldagainst one another tightly yet insulated electrically.
 13. The directcurrent machine of claim 11, wherein the permanent magnets are formed ineach case as rod magnets, the opposite ends of which are held, in eachcase, in one seat in the respective pole shoe formed at least partiallyin a complementary fashion to the end of the rod.